1. Field of the Invention
The present invention relates to a catalyst for polymerizing an aromatic vinyl compound, and a process for producing a polymer of the aromatic vinyl compound. More particularly, the present invention relates to a catalyst and a process for producing an aromatic vinyl compound polymer mainly in the syndiotactic configuration with high catalyst activity.
2. Discussion of the Background
Polymers of aromatic vinyl compounds include polymers of three types of configuration, namely syndiotactic, isotactic and atactic polymers. Among them, polymers of syndiotactic configuration are useful as heat-resistant polymers because of the higher melting point and the larger crystallization rate in comparison with polymers in other types of configuration.
A syndiotactic aromatic vinyl compound polymer was produced, for example, by employing a catalyst composed of a titanium compound such, as a titanium halide, and alkoxytitanium and a reaction product of an organoaluminum compound with a condensing agent such as a methylaluminoxane as disclosed in Japanese Patent Application Laid-Open No. Sho 62-104818. The catalyst systems of the prior art, however, exhibit unsatisfactorily low catalytic activity, and require substantial improvements in the catalyst activity.
Additionally, methylaluminoxane which is a reaction product of an organic aluminum compound with water, as a condensing agent is extremely expensive, so that the amount to be used of the methylaluminoxane is desired to be low in view of the cost.
The inventors of the present invention have made a comprehensive study to solve the above-mentioned problems, and found that use of a specific catalyst system enables production of an aromatic vinyl compound polymer mainly in the syndiotactic configuration with high catalyst activity.